A nice refinement to the "dump and sort" method was published in City Farmer, a publication of Canada's Office of Urban Agriculture.  Their site is jam-packed full of good information on urban agriculture.  When you're finished there, be sure to use your browser's "Back" button to return here.  We'll leave a light on!

This method is very old.  It works by setting up vibration in the bin, so that the worms think it’s raining and come to the surface to avoid drowning.  One way is to take a broomstick, press one end against the bottom of the bin, and roll it between your hands.  A more modern way is to place the bin on a clothes dryer and turn it on for 5 seconds.  Not recommended!